How to prepare for extreme weather conditions in the built environment

We’ve experienced every weather condition imaginable over the last few weeks - from an extreme heat wave across Europe to heavy rainfall causing flooding chaos across the UK. These conditions are a reminder of how important it is to factor eventualities relating to climate change into everything we do in the construction industry. Particularly in the glamorous area of drainage. With more than 12 years' experience in engineering, I’ve seen how the industry has adapted to prepare for flood risks, rising sea levels - and more. Climate change is a very real threat and one that we need to be ready for. Sustainable development – and particularly drainage – is a good place to start.

What are we doing already to prepare for flood risks?

More and more, developments are taking shape on areas associated with flood risk. The EA claims that: 'properties built in the floodplain are likely to double over the next 50 years...' and that: '...all new development must be resilient to flooding and coastal change'. We're working with architects, developers and local authorities to advise on how best to prepare for this. Building on flood plains is a risk, but it doesn’t have to be if it's mitigated properly. We have worked on a number of projects where we have incorporated flood voids - spaces below buildings that allow water to flow and be stored, preventing the loss of floodplain storage. These mitigate any potential risk of flooding downstream of a proposed site. Drainage elements - like flood voids - need to be developed collaboratively with the architects at an early stage to ensure a solution is provided that doesn’t need a redesign during the detailed design stage. Preparing for excess rainfall in all drainage designs is now seen as standard industry-wide. Three years ago, we would use a rainfall intensity figure of +30% - stipulated within the National Planning Policy Framework’s (NPPF) technical guidance - as a precautionary response to climate change’s impact on rainfall intensity. However, today we're committed to using +40%. This increased figure comes from the EA, following Met Office research. A 10% increase in the space of just three years is significant and has further shaped drainage design in preparation for the future, with research still going on to interrogate this figure and ensure that the industry doesn’t remain complacent. Rising sea levels are also a big concern for the EA. And rightly so. A recent project we worked on was only 25m from the coast line, with sea levels the primary concern for the Local Lead Flooding Authority (LLFA). In addition to the everyday design principles involved within drainage design, we were further challenged to consider the effects of rising sea levels and mitigating any impact this may have on the proposed development. Ensuring our proposals met with the LLFA requirements, while also producing a feasible design for the client was a challenge, but also a great opportunity to educate ourselves further in our profession.

What can we be doing next to prepare for flood risks?

The question clients will often ask is: what's the cost? Sustainable design isn't always cheap, but it's necessary. Costs are offset in the long run. Designing better buildings means that unexpected issues aren't encountered later down the line so, although it may cost more upfront, it will save money in the long run. Drainage design no longer means catering for a proposed development’s immediate needs. It means designing for the future and ensuring that all regulating authorities are satisfied that flooding will not occur further downstream on another development. We have to consider existing drainage networks and infrastructure. With a new development, we need to ensure that a new system will not have an adverse effect on the existing network already in place, whilst also providing a solution which takes into consideration the constraints the site has. SUDS features (sustainable drainage systems) play an increasingly big role here.

Drainage can't change the world. Can it?

Of course, I'm biased but drainage is a crucial element of development and can make or break a planning proposal. At Dice, we provide; Upfront, high level analysis of proposed developments - this means that a client knows exactly what potential issues may arise with the site and how the SUDS hierarchy is increasingly becoming a must to follow from the LLFA. Detailed drainage strategies - as opposed to designs just to get through planning, we provide designs with significant enough detail, to ensure the client doesn’t get any (costly) surprises at detailed design stage. We use relevant, up-to-date climate change allowance levels to future proof the site. The Environment Agency (EA) has announced a major, long-term strategy to tackle flooding and coastal change. Read more about its consultation on the subject here: https://consult.environment-agency.gov.uk/fcrm/national-strategy-public/